- This video will present tech tips for Lab 11 for your chemistry investigations
for use with AP Chemistry Lab Book, using the SpectroVis Plus Spectrophotometer. In
this kinetics experiment, you will be exploring the reaction between solutions
of crystal violet and sodium hydroxide. One of your goals will be to write the
right law for the reaction. As you can see in this demo, the purple color of the
crystal violet fades as the reaction proceeds.
One way to measure the rate of the reaction is by spectroscopy to follow the
fade in color. A SpectroVis Plus Spectrophotometer can be used to measure
the fade in color. There are many wavelengths with which to choose. Your lab
group will choose a wavelength that gives you the best data to analyze this
reaction. I'll show you how to set up the SpectroVis Plus with a LabQuest or a
computer. Let's work with a LabQuest 2 first. After you've connected the
spectrometer to the LabQuest, plus the blank cuvette filled with distilled water
in the spectrometer. On the meter screen, tap Sensors, and choose Calibrate, and
choose Spectrometer. The screen will change and a 90 second timer will start.
Since I've connected the spectrometer for more than 90 seconds, I will skip the
warm-up and finish calibration. And then tap on OK to complete the action. Now,
we'd like to take a look at the graph of the available wavelengths and absorbance
value for a solution of crystal violet. Remove the blank cuvette and insert a
cuvette of the crystal violet solution. Tap on the green arrow to start data
collection. You will see a graph of data. Tap on the red square to stop the data
collection. Next, you will choose a wavelength to use as you follow this
reaction. Move the cursor along the graph to choose a wavelength. The exact
wavelength where your cursor rests will be displayed to the right of the graph. Now
you will set up the data collection mode. Go to the meter screen, tap on the gray
mode box, and screen changes. Tap on mode and choose time-based. Decide on an
interval and duration for your data collection, and make any necessary
changes. You can do a trial run and use the default settings to check how long the
reaction proceeds, and how often you should record a reading of absorbance from
the spectrometer. I'll be using the default settings and tapping on OK to
complete the action. You will now be prompted to save or discard your graph of
wavelength versus absorbance. This is your choice and whatever you choose will not
affect the rest of your experiment. Check the wavelength displayed in the meter box.
If you need to change it, tap on the meter box and choose change wavelength. Type in
the wavelength you want, and tap on OK. We're now ready to run the reaction. Mix a
measured amount of the reactants, transfer some of the reaction mixture to the
cuvette, and place the cuvette in the spectrometer, and then start your data
collection.
Here are some sample results. To point out, 500 nanometers may not be the best
choice, and you will have to decide amongst yourselves as a group what will be
the ideal wavelength for this reaction. Then to save this run and get ready for a
second trial, tape on the file cabinet icon. And you'll be ready to collect your
second trial. The next part of this video, we'll go over the same information but
using a computer for data collection. To use a SpectroVis Plus with the computer,
use a standard USB cable to connect it directly to your computer, launch Logger
Pro 3 software on your computer, and next we'll calibrate the spectrometer. Place a
blank cuvette filled with distilled water in the spectrometer. And in Logger Pro,
open experiment menu, and choose calibrate, and then choose spectrometer.
You will see a small dialog box, and a 90 second timer will start. This spectrometer
has been already connected for the 90 seconds, so I will skip the warm-up. And
then I'll tap on finish calibration. And then click on OK to complete. Now we will
graph wavelength versus absorbance for crystal violet. Remove the blank cuvette
and insert a cuvette of crystal violet solution. Start the data collection by
tapping on the green arrow or collect button. You will see a graph of data. Stop
data collection. Next, we will choose a wavelength to use to follow the reaction,
and chose a mode of data collection. Click on the configure spectrometer icon in the
toolbar. Choose absorbance versus time as the collection mode. And to choose a
wavelength, first click on the clear selection button on the list of
wavelengths. To choose your wavelength, choose one from the list or click on the
graph in the dialog box and then click OK. At the prompt, decide whether or not to
save your graph of data. We're now ready to run the reaction. Mix a measured amount
of the reactants, transfer some of the reaction mixture to a cuvette, place the
cuvette in the spectrometer, and then start the data collection.
One you've collected all the data, you can save the run, and get ready for your
second trial. Open the experiment menu and choose store latest run. For more
information on the use of SpectroVis Plus, please visit the Vernier website.